1. Field of the Invention
This invention relates to an apparatus for applying a flexible adhesive strip around the perimeter edge of a rigid substrate. More particularly, the present invention relates to an improved apparatus for applying an insulating edge strip onto glass sheets as part of the manufacturing process of insulating glass units.
2. Description of the Prior Art
To simplify the production of insulating glass units, various adhesive strip products have been developed. One such product is described in U.S. Pat. No. 4,831,799. The product is manufactured from flexible thermoset rubber foam that incorporates desiccant fill material and features a vapor barrier backing film and acrylic side adhesive. The side adhesive is protected by a flexible release liner that allows the material to be packaged on reels. This adhesive strip product has been commercialized by Edgetech IG Inc., and is marketed under the registered trademark name of SUPER SPACER.RTM..
For the production of insulating glass units, the adhesive strip product is applied around the perimeter edge of a glass substrate. To provide continuity of the vapour barrier at the corners, a notch is made at the corners and this creates a flex point that allows for easy corner formation.
Various application tools have been developed for forming these notched corners and as documented in photographs of a prototype Edgetech application tool, one way of forming these corner notches is through the use of a slidable circular punch. The Edgetech tool incorporates various special features including: strip feeding channel, alignment guide, cylindrical handle, pressure wheel and pneumatic cylinder punch.
When activated, the hollow punch removes a half circular portion or slug of strip material. Because of the acrylic side adhesive, these slugs adhere together and consequently, the slug material can be easily ejected from the tool. As a result, the tool can remain in continuous contact with the glass sheet and the productivity of strip application is improved.
At the final corner, there can be further productivity advantages if the tool can also incorporate a blade for cutting through the adhesive strip. As described in U.S. Pat. No. 5,472,558 issued to Lafond, one approach is to add a separate blade that operates in combination with the punch to both notch and cut through the adhesive strip at the final corner. Although productivity is improved, experience has shown that this simultaneous operation of the punch and cutting blade requires a complicated punch design that is expensive to manufacture and is prone to wear and damage.
Compared to the earlier Edgetech tools, another new feature of the Lafond tool is that both the pneumatic cylinder and strip feeding channel are steeply inclined at angle and this has the advantage of a reduced channel length between the pneumatic cylinder and the pressure wheel. However, the drawback is that after strip cut-off, the tool requires to be rethreaded and this can be a time consuming operation.
The Lafond tool also features a cylindrical handle and a finger trigger for operating the pneumatic cylinder that is located below the handle and operated by means of a finger pulling action. From an ergonomic perspective, and for horizontal strip application using a rotary table, there are three main drawbacks to this arrangement. First, it provides for wrist deviation with rapid finger movement. Second, it combines forceful gripping with a twisting action and third, it requires rapid and forceful pronation with strong elbow and wrist flexion.